1. Field of the Invention
This invention relates to a plug assembly for data transmission, and to a method of wiring the same. The preferred embodiment of the invention provides a plug suitable for category 6 data transmission installations which provides reduced near end and far end cross-talk levels as compared with conventional data transmission plugs.
2. The Prior Art
The use of mating plugs and jacks in data transmission installations is well known. As data transmission rates have increased more care has been applied to the design of all plugs and jacks in order to reduce to a minimum cross-talk induced by the plugs and jacks. Various schemes have been proposed for substantially reducing the cross-talk induced by a jack including, in particular, the use of cross-talk cancelling components on the circuit board to which the jack is conventionally secured.
Dealing with the problem of the cross-talk generated within the plug has proved more difficult. In this context, it must be remembered that the plugs in question are inherently of small size and they are required to have an array of parallel contacts for mating with corresponding contacts in the jack. The array of parallel contacts itself induces cross-talk within the plug. Further, the need to untwist the usually twisted pairs of conductors in order to connect the individual conductors to the contacts induces further cross-talk. Because of the small size of the plug, the techniques used for the purposes of reducing cross-talk in jacks cannot be applied directly to the plug. To an extent, the cross-talk induced by a plug may be cancelled by appropriate selection of cancellation components on the circuit board of the jack into which the plug is inserted. Unfortunately, however, the cross-talk induced by a plug tends to be very variable, at least in part as a result of the variations in positions of the conductors within the plug. Accordingly, including cross-talk cancelling components on the jack circuit board cannot be used reliably as a method of compensating for cross-talk induced in a plug inserted into the jack.
Typically, a plug may have eight contacts which are separately connected to the conductors of four twisted pairs of conductors. For the purposes of this discussion the conductors of the first twisted pair are designated A and B; the conductors of the second twisted pair are designated C and D; the conductors of the third twisted pair are designated E and F; and the conductors of the fourth twisted pair are designated G and H. By convention one conductor of each pair is coloured to identify the pair and the other conductor of each pair is predominantly white but has bands of colour corresponding to its associated coloured conductor. For the purposes of this discussion conductors A,C,E and G will be considered to be coloured conductors and conductors B,D,F and H will be predominantly white conductors. In standard four twisted pair cables the coloured conductors are coloured brown, green, blue and orange and for the purposes of this description conductor A will be regarded as,the brown conductor, conductor C will be regarded as the green conductor, conductor E will be regarded as the blue conductor and conductor G will be regarded as the orange conductor. It follows from the above that conductor B will be predominantly white but with brown bands, conductor D will be predominantly white but with green bands, conductor F will be predominantly white but with blue bands and conductor H will be predominantly white but with orange bands.
In the standard and enhanced version of the common RJ45 plug the conductors are connected toga linear array of eight parallel side-by-side contacts. The common 258A and 568B wiring conventions require the conductors to be connected to the contacts so that the conductor order, measured from end to end of the linear array, is ABCFEDGH. This arrangement is recognised as reducing the cross-talk particularly between the CD pair and the EF pair.
RJ45 type plugs still, however, produce a significant amount of cross-talk which in turn makes it very difficult to produce plugs which satisfy category 6 cross-talk standards. Cross-talk is largely induced by the parallel array of contacts within the plug and by the fact that the conductors must run parallel to each other in the zone immediately adjacent the connection to the contacts. The problem of cross-talk is further complicated by the fact that the individual conductors are, at the present time, to an extend randomly located within the plug body. As a result, although some plugs may attain an acceptable cross-talk level, others which are nominally identical do not. As noted above, the variation between plugs of nominally identical design also renders it impracticable to compensate for plug cross-talk by means of additional components associated with a jack socket of the circuit board on which the jack socket is mounted.
We have now found that the cross-talk induced in a plug can be reduced if, in a region between the contacts and the point where the cable enters the plug, the conductors of the CD pair and the conductors of the EF pair are constrained to run with the C and E conductors adjacent each other.
In one embodiment the D and F, conductors are also constrained to run adjacent each other. In other words, in a region adjacent the contacts the conductors of the CD and EF pairs are constrained to run with the conductors which are connected to pins 3 and 5 close to each other and the conductors which are connected to pins 4 and 6 close to each other.
We have devised a number of plug arrangements which utilise this routing of conductors C,D,E and F to reduce cross-talk. The different plug arrangements provide different degrees of cross-talk reduction. Whilst in many applications a plug which produces the maximum reduction in cross-talk will be required, other applications which are less demanding may utilise less efficient embodiments of the invention.
In addition to reducing cross-talk, the preferred embodiments of the present invention provide accurate control for the position of the conductors within the plug. As a result, plugs according to the preferred embodiment of the invention provide more consistent levels of cross-talk than similar plugs of the prior art. As a result, to the extent that cross-talk is produced by the plugs in the preferred embodiment this can, to an extent, be compensated for by a design of the jack or jack mounting board with which the plug is, in use, to be associated.
The desired arrangement can conveniently be achieved by use of a wiring manifold as part of the plug assembly.
In one embodiment of the invention the wiring manifold defines two channels, one for receiving the D and F conductors and the others for receiving the C and E conductors. In this embodiment the AB pair and the GH pair bypass the wiring manifold and remain as respective twisted pairs as they pass the zone of the wiring manifold. Preferably, the wiring manifold and an associated load bar include inter-engaging latching means whereby the wiring manifold is, in use, secured to the load bar. Preferably, the wiring manifold is of a polycarbonate material, although in some embodiments of the invention a relatively soft and flexible material, for example silicone rubber, may be used.
In another embodiment of the present invention we have found that cross-talk induced in a plug can be reduced if, in the region between the contacts and the point where the cable enters the plug, the conductors of the CD pair and the conductors of the EF pair are constrained to run with the C and E conductors adjacent each other and with the F conductor adjacent the E conductor and the D conductor adjacent the C conductor. In a particularly preferred arrangement the C and E conductors are located one above another; and the F conductor is at substantially the same level as the E conductor. In one embodiment the F conductor is located to one side of the vertical plane passing through the C and E conductors, and the D conductor is at the same level as the C conductor and on the opposite side of the said plane from the F conductor. In another embodiment the C and E conductors are located in one vertical plane and the D and F conductors are located in a second vertical plane parallel to the first vertical plane. In this arrangement the D conductor is at the same vertical level as the C conductor and the F conductor is at the same vertical level as the E conductor. Preferably, the spacing between the C and D conductors is the same as the spacing between the C and the E conductors which is in turn the same as the spacing between the E and the F conductors which is in turn the same as the spacing between the F and the D conductors. In the preferred embodiment of the invention when the plug is viewed in transverse cross section, the C,D,E and F conductors are located at the respective corners of a square with the C conductor diametrically opposite the F conductor and the D conductor diametrically opposite the E conductor.
In one embodiment of the invention a wiring manifold is provided which includes three channels. The centre channel holds the C and E conductors adjacent each other with the C conductor above the E conductor. A second of the channels is located offset to one side of the first channel and holds the F and G conductors with the F conductor located, adjacent the E conductor. The third channel is located offset to the opposite side of the first channel and holds the D and B conductors with the D conductor adjacent the C conductor. The second and third channels are vertically offset from each other so that the F and G conductors are at the same level as the E conductor and the D and B conductors are at the same level as the C conductor.
Preferably, tie wiring manifold includes channels in the outer surface thereof to guide the A and H conductors. The guide for the H conductor is preferably located vertically above the G conductor and the guide for the A conductor is located vertically below the B conductor. This arrangement has been found to give particularly advantageous cancelling results when used in an enhanced RJ45 plug. Preferably, the body of the plug includes a portion or a separate load bar member which defines eight side-by-side parallel passages each for a respective one of the conductors. With such an arrangement, after the respective conductors exit their channels in the wiring manifold they can be directed as necessary through the passages in the load bar to be presented to the contacts in the correct order.
In another embodiment of the invention a wiring manifold is provided which defines six channels. Five of the channels are designed to carry one conductor whilst the sixth channel is designed to carry three conductors in a side by side arrangement. With such a wiring manifold the C and E conductors are constrained to run parallel to each other through the wiring manifold one above the other. The G and the H conductors pass through the same channel as the E conductor with the H conductor located between the G conductor and the E conductor. The E and F conductors pass through respective side by side channels with the E conductor adjacent the C conductor and the D conductor adjacent the F conductor. The A and B conductors run through respective channels located at the opposite extremity of the wiring manifold from the channel for the E, G and H conductors. In cross-section, and viewed from the rear of the plug, the wiring manifold preferably constrains the B, D and C conductors to run parallel to each other in one horizontal plane with the D conductor located between the B conductor and the C conductor, and the remaining conductors to run parallel to each other in a second horizontal plane spaced from the first horizontal plane with the A conductor at one extremity, the G conductor at the opposite extremity, the F conductor next to the A conductor, the H conductor next to the G conductor, and the E conductor between the F conductor and the H conductor.
In a preferred plug and cable assembly according to the present invention the cable includes a cruciform separator for separating the respective twisted pairs of conductors. The separator terminates within the sheath of the cable a short distance from the sheath end and the wiring manifold is partially inserted within the cable sheath so that the rear of the wiring manifold abuts or is close to the end of the separator. As a result, the transition from the twisted pair and separator arrangement which exists over the majority of the length of the cable to the wiring manifold is well controlled with minimal opportunity for variation in cable position. Preferably, the cable sheath is clamped to the wiring manifold.